The great American road trip is a clever narrative device that hasn't gotten old since Huck and Jim were rafting down the Mississippi River. Take some guys-or gals, as in "Thelma and Louise"-with great chemistry, give them a mundane or ridiculous task-consider the newspaper assignment Raoul Duke was on for "Fear and Loathing In Las Vegas" or that of the underage girl from the same work who was hoping to present Barbra Streisand with her art-and set them rolling along. The device works best for comedy, as the pacing and intrinsic timing of it make it easy to introduce new characters and settings if the old ones have stopped working for whatever reason.

Director Todd Phillips has put that dynamic to good use in "The Hangover." It's witty, paced well, and rides its lead characters for every drop of chemistry between them. The plot of "The Hangover" definitely orbits around the ridiculous quest end of the spectrum. In it, three groomsmen lose their friend in Las Vegas-Las Vegas is a perennial favorite among road trip movies-and, having no memory of what they did or of where they've been, they have to retrace their steps to find him in time for the wedding. Of course, this is a rich vein to mine, character-wise, and brings the trio up against some of the most absurd supporting characters and premises of any recent comedy.

Phillips really knows what he's doing when he puts Bradley Cooper, Ed Helms, and Zach Galifianakis together on a quest. As with any actors, there are certain strengths to their performance styles as well as weaknesses. Zach Galifianakis, for example, is simply incapable of being serious for any length of time. When he tries, the result feels like trying to suppress a laugh in church. The harder he tries to emote gravity, the harder he's going to drive the audience into that frozen zone of totally inappropriate laughter. A smart director will recognize this shortcoming-and it is a shortcoming, even in a comedy-and, rather than try to change his raw material or shoehorn his talent into the wrong pigeonhole, he'll work with it and just put Galifianakis in scenes where he doesn't have to be even slightly serious.

Another potential hurdle Phillips narrowly manages to avoid is the inherent difficulties of bringing on somebody who really isn't an actor to act the heck out of a scene. Usually this involves some kind of a cameo, such as that time Melvin Belli made a surprise appearance on a late-season episode of "Star Trek." This can end in disaster, as the person talked into doing a cameo can sometimes fail to deliver any detectable conviction and goes hurtling through the fourth wall so hard he leaves plaster on the floor of the theater. It takes a skilled and experienced director to avert this, and just about the highest compliment that can be paid to Phillips is this: he indisputably made Mike Tyson believable in his cameo.

While the key elements of "The Hangover" are all in place and nothing seems especially jarring or out of place, it's unfortunately true that some other aspects of this film left something to be desired. The film's score is jarring at times and will occasionally take a polite leave of absence from whichever scene it's been written for. Some of the dialogue uttered by peripheral characters is flat and unconvincing, suggesting multiple rewrites. Here and there, a continuity error sneaks into the frame, only to disappear in the next shot.

None of these shortcomings are fatal, of course, and none of them are even especially odd or unusual for a movie. Certainly none of them come close to derailing what will always be the beating heart of a movie like "The Hangover": the indefinable sparkle that exists between two or three well-matched actors who manage-after a million takes, no doubt-to drop any sense of their protective mask and just start hanging out together on the great American road trip.

"The Hangover" isn't a pretentious film. It never makes an effort to be anything other than what it was always meant to be: a light comedy about three dudes who figure out that it's time to start growing up on the morning they awake to realize they've stuck their best friend somewhere and can't remember where he is. All that being said, Bradley Cooper, Ed Helms, and Zach Galifianakis are to be commended-and Todd Phillips deserves a medal of some kind-for keeping this project on-task, and for bringing it in without giving in to the temptation to include a bunch of slow, ponderous drama, which has traditionally been the cause of second act death syndrome.